Multi-battery charging system for reduced fuel consumption and emissions in automotive vehicles

ABSTRACT

A multi-battery charging system for reduced fuel consumption and emissions for an automotive vehicle. The system starts the vehicle with a start battery in a fuel saving manner, removing electrical torque from the alternator shaft, and allows a second (run) battery to provide all or some of the current required by the vehicle loads as a fuel savings measure. The start battery is recharged after start and switched out of the system fully charged for future vehicle starts. The run battery is recharged when its charge level drops below a predetermined level with an on board battery charging device powered from a 115 volt or 220 volt ac power line source external to the vehicle. The system also increases the alternator field current to charge the run battery during vehicle deceleration to use vehicle momentum to torque the alternator shaft, thus saving fuel. The system controls the alternator field current with a voltage regulator. The voltage regulator senses the charge level of the run and start batteries and vehicle operating conditions and provides the proper current into the alternator rotor for maximum fuel savings. The voltage regulator may be a non-microprocessor or a microprocessor controlled device.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 07/919,011, filed Jul. 23, 1992, in the name of Wesley A.Rogers and entitled An Improved Battery State of Charge Monitor, whichis a continuation-in-part of U.S. patent application Ser. No.07/607,237, filed Oct. 31, 1990, in the name of Wesley A. Rogers andentitled Apparatus for Monitoring the State of Charge of a Battery, nowissued as U.S. Pat. No. 5,179,340, which is a continuation-in-part ofU.S. patent application Ser. No. 07/218,539, filed Jul. 13, 1998, in thename of Wesley A. Rogers and entitled Apparatus for Monitoring the Stateof Charge of a Battery, now issued as U.S. Pat. No. 4,968,941.

FIELD OF THE INVENTION

This invention relates to a multi-battery operating system forautomotive vehicles that provides improved fuel economy and reducedemissions during operation and during starting, more particularly athree battery system having a start battery for starting the vehicle, arun battery for providing the vehicle load and accessory current, and astorage battery for preheating a catalytic converter during starting.

BACKGROUND OF THE INVENTION

In the normal operation of an automotive vehicle, a fully charged sixcell battery having between 2.05 and 2.1 volts per cell (hereinafterreferred to as a "start" battery) is used to start the engine and tooperate accessory loads when the engine is not running. The conventionalstart battery is well suited to provide large start currents to thestart motor on the order of 150 to 250 amperes.

The start battery is provided with thin plates between its individualcells that provides for a rapid, large current, shallow discharge duringvehicle start. Unfortunately, the start battery cannot be deeplydischarged in a repetitive manner without damaging the thin cellseparator plates.

It has long been the practice to provide an alternator driven by theengine that can be used to recharge the start battery after vehiclestart and provide current to both the vehicle run and accessory loads.It has also been the practice to maintain the alternator chargingvoltage at a nominal value of 14.0 volts at an ambient temperature of 85degrees F. The nominal value is raised to 14.6 volts at minus 20 deg. F.and lowered to 13.6 volts at 140 deg. F. This provides adequate chargecurrent as a function of ambient temperature and thereby extends batterylife.

A voltage regulator is used to inject a controlled current into thealternator rotor. This in turn provides a controlled current in thestationary (stator) field coils. This in turn yields the rectified dcoutput voltage required for battery recharge after start and to supplythe required vehicle load currents.

OBJECTS AND SUMMARY OF THE INVENTION

It has been realized by the inventor that the conventional operation ofa start battery and alternator based electrical system of an automotivevehicle wastes energy. First, the alternator requires the engine toprovide fuel consuming torque to operate the alternator at a nominalvalue, e.g., a 14.6 volt dc output level, in order to recharge the startbattery and provide the required current to the vehicle loads. Second,the vehicle electronic circuits contain power consuming voltageregulator circuits that reduce the alternator output voltage to a 12 or5 volt level. Third, the alternator places a mechanical torque on theengine as a function of the alternator output voltage and the currentdrawn to supply the load requirements and to charge the start battery.The fuel consumed by the engine to overcome the alternator countertorque is an unnecessary expense. Fourth, the vehicle engine andalternator are substantially less than 100% efficient and consume acorrespondingly greater amount of fuel.

In addition, the inventor has realized that if the state of charge ofthe vehicle batteries are reliably and accurately determinable overtheir useful life it is possible to control the alternator outputvoltage, as required, either to charge the vehicle batteries or to allowone or more batteries to provide all the current required by the vehicleloads.

It is a further object of the invention to increase alternator outputvoltage during deceleration of an automotive vehicle, thereby usingvehicle momentum to provide an increased torque load that is used tocharge a battery.

It is another object of the invention to turn off selected vehicleaccessory loads when the vehicle is parked and to turn off selectedvehicle accessory loads when the state of charge of the batteryproviding current drops below a selected level.

It is another object of the invention to provide a storage battery forproviding the current required to heat an electrically heated catalyticconverter (EHC) during or prior to vehicle start when the enginetemperature is below a selected level.

In accordance with the present invention, apparatus, systems, andmethods are provided for providing sufficient electrical power to startand run an engine, to reduce the energy expended and fuel consumed andassociated emission by-products in starting and running the engine, andoptionally in operating a battery charging device to maintain asufficient charge on each battery for the range of operating loadconditions.

One aspect of the invention concerns a battery charging and run systemfor starting the engine of an automotive vehicle and operating theelectrical loads of the automotive vehicle with improved fuel economy.

One embodiment of this aspect of the invention concerns a batterycharging system for an automotive vehicle having:

a start battery for use in starting the vehicle engine;

a run battery for operating the vehicle accessory and non accessoryloads;

a battery charging device, such as an alternator, having a controllableoutput voltage when the vehicle is running;

a first BSOC channel for monitoring the state of charge of the start ofbattery;

a second BSOC channel for monitoring the state of charge of the runbattery; and

a first circuit, such as a voltage regulator, for controlling the outputof the battery charging device to provide one of a first output voltagethat varies in a first range as a function of ambient temperature whenthe sensed start battery state of charge level is below a first chargelevel and a second output voltage when the battery state of charge levelis above the first charge level, a third output voltage to recharge therun battery when the run battery state of charge is below a secondcharge level, and a fourth output when the run battery state of chargeis above the second charge level.

Preferably a switch is provided to switch the start battery out of thesystem after it is recharged. The switch is responsive to the sensedstate of charge of the start battery and open circuits the start batteryupon reaching the first charge level. In operation, the start battery isemployed to start the vehicle engine. Its state of charge thus fallsbelow the first charge level (corresponding to the prestart chargelevel). This causes the control circuit/voltage regulator to control thebattery charging device to provide a first output voltage to rechargethe start battery, e.g., between 16.4 and 13.6 volts dc, according tothe ambient temperature in the conventional manner. When the sensedstate of charge of the start battery is at the first charge level, thecontrol circuit/voltage regulator may then control the battery chargingdevice to provide the second output voltage level to maintain a fullcharge on the start battery. In a preferred embodiment, the switch isconfigured to respond automatically to the start battery state of chargereturning to the first charge level and switch the start battery out ofthe charging system in a fully charged state. Alternatively, the switchmay be manually operated by the operator who acts in response to aprompt, such as a light, audible tone, or battery state of chargedisplay. When the start battery is switched out, the two battery systemthen may operate in one of two modes. In the first preferred mode ofoperation, the automotive vehicle electrical load is run off the runbattery entirely. In this mode, once the start battery is switched out(and, as described below, an EHC battery is switched out), the controlcircuit controls the battery charging device to provide the fourthoutput by reducing the field current until the bridge rectifier diodesbecome back-biased. When the control circuit is a controllable voltageregulator, the battery charging device is an alternator, and the voltageregulator output into the alternator rotor coil is about zero, there islittle, if any alternator counter torque on the engine and the rectifiedalternator output bridge diodes are backed biased and provide nocurrent. Accordingly, the run battery will discharge to operate thevehicle load. During this discharge, the absence of the alternatorcounter torque results in improved fuel economy.

However, when the state of charge of the run battery falls to the secondcharge level, which corresponds to a low charge (deep discharge) levelthat will not damage the run battery, the control circuit/voltageregulator controls the battery charging device to provide the thirdoutput voltage. The third output voltage is then used to provide powerfor the vehicle load.

The third output voltage level may be selected as follows. It may be alevel that will power the vehicle load and maintain the run battery atthe second charge level. This selected level may be adjusted to preventany further reduction in the state of charge of the run battery. In thiscase, the third output voltage may be on the order of 12 volts, asadjusted for ambient temperature conditions. Alternatively, the thirdoutput voltage may be a level that will power the vehicle level andrecharge the run battery to a fully charged state, e.g., a voltagebetween 13 and 14.6 volts dc, as a function of ambient temperature. Oncethe run battery is recharged, it is allowed to discharge down to thesecond charge level, during which time the vehicle loads are again runexclusively off the run battery. Thus, whenever the alternator outputvoltage is reduced from the conventional full charging state, thealternator counter torque on the engine is less and there is improvedfuel economy.

In all cases, the run battery is preferably recharged using aconventional battery charger which is powered from an external linesource, e.g., a 220 or 115 volt ac line power supply. This permitsreplacing the amp-hour charge that was removed from the run battery bythe vehicle loads with a source of electricity external to the vehicle.The external electricity source typically costs less per unit of energythan petroleum and alcohol based fuels and avoids consuming theincremental fuel that was saved during discharge of the run battery togenerate the power needed to recharge the run battery. Such a batterycharger may be mounted on or off the vehicle.

In another mode of operation, after the start battery and run batteriesare recharged, the start battery is switched out and the batterycharging device is operated to provide a fifth output voltage level andcurrent for operating the vehicle accessory load. The fifth outputvoltage level is preferably selected to provide just enough current tooperate the vehicle accessory loads, e.g., 12 volts for a 12-volt systemand also applies a trickle charge current on the run battery. This modealso reduces the energy consumed as compared to prior voltage regulatorstart battery alternator systems that always produced more voltage thanwas required by the vehicle loads.

Switches and control circuits may be used to control automaticallyand/or manually the battery charging device and to connect selectivelythe battery charging device to one or both of the run and startbatteries, and to provide the desired output voltage(s) and current(s)to recharge the batteries, singly or jointly, to operate the accessoryand non accessory loads. A microprocessor may be used to control thevarious battery state of charge monitors, control circuits, andswitches. Alternatively, a logic circuit network or a state machinecomprising discrete and solid state components may be used as a controlcircuit. In addition, an operator display and manual switching systemmay be used.

Another aspect of this invention concerns providing a switch to connectone battery in place of the other battery if one of the batteries shouldfail to hold an adequate charge, and to use both batteries in parallelor in series when conditions so require. This is particularly useful invery cold weather when an additional source of start current is desired,and where one battery either fails or is not fully recharged before theengine is turned off.

Optionally, a measure of the amplitude and direction of the current flowinto or out of the run battery or the start battery may be included fordecision making purposes in selecting a voltage level. A large startbattery discharge current may confirm a starting operation and raise thealternator output voltage level. An increased flow of current out of therun battery, i.e., a load current that might deplete charge from the runbattery if the trickle charging voltage was maintained, could result inraising the trickle charging voltage, the load current and the batterystate of charge.

Preferably, the start battery is a conventional automotive batteryhaving thin cell plates and the run battery is a deep discharge, marineor cycle-proof battery. Such run batteries have thick cell plates andcan be deep discharged to levels repeatedly, without seriouslyshortening their useful life. The thick plate construction also allowslonger operation as an energy source than comparable thin cell platestarter batteries. However, run batteries typically cannot develop thehigh discharge currents suitable for starting the engine of anautomotive vehicle. Other types of run batteries which are capable ofrepeated deep discharge are becoming available and may be used. Forexample, Ford Motor Company has announced such a high charge storage runbattery for use in its forthcoming electric vehicle. Other batteries,such as sodium sulphur batteries having increased amp-hour ratings, ascompared to lead acid batteries, also may be used. Further, when deemedappropriate, the size of run battery 20 may be reduced to a five cellbattery to have a 12 volt rating or increased to 24-25 volt with a DC/DCconvertor to increase the time for running off run battery 20, and toreduce the size of the alternator.

Advantageously also, it has been discovered that a fuel and cost savingscan be achieved by the reduced alternator mechanical load on the engineand lower fuel consumption whenever, and to the extent that, thealternator field current is decreased to back bias the output rectifierdiodes. Another advantage results from recharging a discharged batteryusing lower cost electricity from a source external to the vehicle.

Preferably, the state of charge of each battery used is monitored by abattery state of charge (BSOC) monitoring circuit channel. Any devicecapable of reliably integrating the net charge over time may be used.Preferably, the BSOC circuit includes a section of the battery returncable as a shunt or a shunt resistor in series with the battery negativeterminal and a circuit having a very large capacitance for integratingthe current through the shunt continuously. See i.e., the circuitsdisclosed in the aforementioned U.S. Pat. Nos. 4,968,941 and 5,179,340and copending and commonly assigned U.S. patent application Ser. No.07/919,011, which patents and application are expressly incorporatedherein by reference in their entirety.

Another aspect of the invention concerns apparatus and methods forcontrolling the charging voltage level applied to a battery in anautomotive vehicle in response to the deceleration of the vehicle.Broadly, this aspect of the invention concerns sensing the decelerationof a vehicle and causing the battery charging device to produce a highlevel charging voltage for rapidly recharging a battery duringdeceleration. When the vehicle is decelerating, the alternator is drivenby the momentum of the vehicle turning the wheels, drive shaft, and,hence, the engine, and not by the engine burning fuel. Thus, duringdeceleration some of the energy stored in the momentum of the vehiclecan be converted by the alternator to energy which is stored in the runbattery.

Accordingly, during deceleration events, the control current to thealternator rotor is increased. This raises the alternator output voltageand results in an increased resistance to rotation of the alternatorrotor coil. As a result, the charge on the battery is rapidly increasedwithout consuming incremental fuel to do so. Another advantage is thatthe increased alternator counter torque load on the engine aids inslowing the vehicle without increased brake wear or effort.

The deceleration feature is particularly useful in stop and go trafficsuch that the battery charging device is turned off during steady stateand accelerating driving conditions and is turned on to provide a highcharging voltage during deceleration. The recharging during eachdeceleration will effectively prolong the time the vehicle can operatesolely off the run battery. It also is useful when operating the batterycharging device at a charging voltage just to maintain a charge on therun battery, for recharging start batteries, whether in the two batterycharging system or a single battery charging system.

During the onset of deceleration, it may be desirable to ramp thecontrol signal to raise the battery charging device output to a highvoltage to minimize slippage and wear on the alternator. A switch may beprovided to disable temporarily the deceleration feature when desired sothat, for example, a driver can coast.

The various aspects of the invention are not limited to battery chargingsystems for automotive vehicles. They are applicable to any apparatushaving a start battery that consumes energy to charge an electricalenergy storage device that is connected to operate an electrical load ordevice, including without limitation, electrically starting combustionengines such as a generator for household (or industrial) current, a gasoperated lawn mower, a powered vehicle or device, aircraft, spacecraft,watercraft, emergency lighting or power plants.

A further aspect of the invention provides a battery which provides avery high current to a heating coil of an electrically heated catalyticconverter (EHC) unit which performs the emission control functions of astandard catalytic converter that is heated by the engine. This batteryis referred to as an "EHC" battery or a "storage" battery. The EHC unitmay be a small catalytic converter that is placed in series with astandard catalytic converter, or it may be incorporated into anotherwise standard catalytic converter by, for example, the introductionof suitable heating coils as a part of the catalytic converter unit.

In operation, the EHC battery is switched, for about 20 seconds, to theEHC unit heater coil during the vehicle start operation. This provides avery high discharge current at a selected level, on the order of 500 to650 amps, preferably 600 amps. The current discharge is high enough forthe heater coil to heat rapidly at the EHC unit to its effectiveoperating temperature and maintain it there during the heating period.The EHC battery may be disconnected after a preset time period, afterthe engine temperature exceeds a selected threshold, or when the stateof charge of the EHC battery falls to a selected charge level. Further,the EHC battery may be switched to the EHC heater until the enginetemperature is suitably high. This provides for preheating the catalyticconverter so that it reaches an effective operating temperature soonerthan conventional catalytic converter systems, which rely solely onengine temperature to heat the catalytic converter. Advantageously, bypreheating the catalytic converter electrically, vehicle emissions aresubstantially reduced during vehicle starting, particularly in coldoperating conditions. A third BSOC circuit channel could be used tomonitor the EHC battery state of charge. If a BSOC channel is used, thecontrol circuit is preferably responsive to the sensed EHC battery stateof change (with appropriate switches) to recharge the EHC battery if itscharge level is below the predetermined level. Provision also is made torecharge the EHC battery with an on or off-board battery charger from asource of 220 or 115 volt ac line power.

Furthermore, the EHC battery may be periodically switched to the EHCheater coil during operating conditions whenever the engine operatingtemperature is insufficient to heat the catalytic converter to itseffective operating condition. This mode of operation may be selectivelyenabled or disabled, and the EHC battery may be recharged whenever itsstate of charge falls below a selected charge threshold.

Although each of the EHC battery system, the two-battery charge system,and the deceleration recharging system may be used separately, they arepreferably combined to provide a more fuel efficient and reducedemission automotive vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and the followingdetailed description of the invention, in which like reference numeralsrefer to like elements, and in which:

FIG. 1 is a block diagram of a non-microprocessor controlled threebattery fuel saving and reduced emission operating and battery chargingsystem in accordance with a first embodiment of the invention;

FIG. 2 is a circuit diagram of a battery state of charge circuit ofFIGS. 1 and 7;

FIG. 3A is a circuit and schematic of a first solid state switch ofFIGS. 1 and 7;

FIG. 3B is a circuit and schematic of a second solid state switch ofFIGS. 1 and 7;

FIG. 3C is a circuit and schematic of a third solid state switch ofFIGS. 1 and 7;

FIG. 4 is a circuit diagram of the thermistor circuits of FIGS. 1 and 2;

FIG. 5 is a circuit diagram of the deceleration circuit shown in FIG. 1;

FIG. 6 is a circuit diagram of the non-microprocessor controlled voltageregulator and alternator of FIG. 1;

FIG. 7 is a block diagram of a microprocessor controlled three batteryfuel saving and reduced emission operating and battery charging systemin accordance with a second embodiment of the invention; and

FIGS. 8 and 9 are measured fuel consumption runs for two differentvehicles under different operating conditions showing load current inamperes versus miles per gallon and indicating the fuel savings obtainedwith the non-microprocessor controlled system of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an apparatus for a three battery charging system inaccordance with a first embodiment of the present invention is shown.The apparatus includes a start battery 10, a run battery 20, an EHCbattery 300, battery state of charge (BSOC) channels 60a, 60b, and 60c,an alternator 40, a voltage regulator 42, a pendulum circuit 70 andvehicle deceleration circuit 90, and an ignition switch 30 includingganged wipers W1, W2, W3 and W4. When wiper W1 of ignition switch 30 isplaced in the start position at contact 32, current is provided fromstart battery 10 on line L1 to start solenoid 31. Start solenoid 31 isthus energized and closes contact 52. This switches start battery 10 tostart motor 50 on line L2 and provides the required current to turn overstart motor 50.

When the engine (not shown) starts, wiper W1 is conventionally returnedto the run position, contact 35. A signal is then applied from startbattery 10 on line L3 through wiper W1 and line L35 that turns on asolid state switch 32SB. When start battery 10 is less than fullycharged, the BSOC channel 60a output on line L25 is low and switch 32SBis conducting. Solid state switch 32SB connects start battery 10 to theoutput of alternator 40 on line L5. This allows alternator 40 torecharge start battery 10. When start battery 10 is recharged the outputvoltage on line L25 from BSOC channel 60a switches to high. A highsignal on line L25 turns switch 32SB off, thus disconnecting fullycharged start battery 10 from the system. A fully charged start battery10 is one that has an arbitrary high percentage of its actual fullcharge, e.g., 90% of full charge.

In the run position, wiper W2 of ignition switch 30 is at contact 34.This connects run battery 20 to output line L5 of alternator 40, tovehicle run load R_(L), and to vehicle accessory load R_(A) throughsolid state accessory switch 34ac. In this condition, run battery 20 isbeing recharged by alternator 40, in the event that it happened to bepartially discharged, and vehicle loads R_(L) are placed across theoutput L5 of alternator 40. For maximum safety, the vehicle lamps,illustrated as HL, are connected directly off both the run and startbatteries 10 and 20 through manual switch S1.

Switch 34AC is controlled by a NAND Gate G2 which receives one inputfrom a "park" position indicator 15 corresponding to the vehicle beingparked (a logical high state), e.g., the shift lever being in the parkposition in a vehicle having an automatic transmission. The second inputis from the BSOC channel 60b output line L7, which indicates when thestate of charge of run battery 20 is above (logical high state) or below(logical low state) the second predetermined charge level. Thus, whenthe vehicle is not in park and the run battery 20 state of charge isabove the preselected charge level, switch 34AC is closed and accessorycircuits R_(A) are switched to battery 20. Otherwise, switch 34AC isopen and circuits R_(A) are switched out. In this embodiment, accessorycircuits R_(A) are noncritical accessory devices the loss of which willnot impair driving safety. A warning alarm device ACW is connected tothe output of NAND gate G2 to produce a visual or audible alarm whenswitch 34AC switches out accessory circuits R_(A). Critical accessoryloads are always connectable to a battery and manually operable, e.g.,headlights.

When run battery 20 has been recharged in accordance with ambienttemperature requirements, the output voltage on line L6 from BSOCchannel 60b switches from a low state to a high state. BSOC channel 60balso has output line L7 which indicates, by changing from high to lowstates, when run battery 20 discharges below a preselected charge level.

When EHC battery 300 is fully recharged, the signal on output line L306from BSOC channel 60c switches from a low state to a high state. At thisevent, the three signals on lines L6, L7 and L306, which are inputs tologic NAND gate G1, are in the high state. NAND gate G1 is a part ofvoltage regulator 42 (see FIG. 6) of which only a portion is illustratedin FIG. 1. (If no BSOC channel 60c is used, NAND gate G1 may have onlytwo inputs, i.e., lines L6 and L7.)

Referring to FIGS. 1 and 6, the above set of high state input conditionscauses the output of NAND gate G1 in voltage regulator 42 to switch tothe low state. This reduces the field current I_(f) in alternator 40 tozero and back biases the bridge rectifier output diodes. This preventsalternator 40 from delivering current to output line L5, which connectsto run battery 20 and the vehicle loads R_(L) and accessory circuitsR_(A). With alternator 40 unable to provide current to line L5, runbattery 20 is required to provide all the current to the vehicle loadsR_(L) and R_(A) until run battery 20 discharges to a predeterminedlevel. When this occurs, the voltage on output line L7 from BSOC channel60b drops from a high to a low state. A low state on line L7 causes theoutput of NAND gate G1 to switch to the high state, thus increasing thefield current I_(F) of alternator 40 from zero to its normal operatinglevel. This forward biases the rectifier diodes. Alternator 40 is nowable to recharge run battery 20 and provide the load current required tooperate the vehicle. During this time, switch 34AC will remain closedwhen the vehicle is not in park and the run battery is above apredetermined charge level.

In summary, the following task sequence is accomplished by the system:

1) started the vehicle with start battery 10 when ignition switch 30 wasplaced in the start position;

2) recharged start battery 10 to its original state, recharged runbattery 20, if necessary, and recharged EHC battery 300 after it hasprovided a 20 second duration 600 amp heater current to an electricallyheated catalytic converter (EHC) 320;

3) switched the alternator 40 out of the system after rechargingbatteries 10, 20, and 30 by reducing field current I_(F) to zero, thuspreventing it from generating current to output line L5;

4) allowed the run battery 20 to provide all the current required online L5 to operate vehicle loads R_(L) and R_(A) under all operatingconditions (except as noted);

5) switched alternator 40 back into the system after run battery 20 wasdischarged to a predetermined level by the vehicle loads R_(L) and R_(A); and

6) recharged the run battery 20 and provided required load currents withalternator 40 in its normal operating state until an external powersource can be obtained.

Preferably, run battery 20 is recharged as soon as possible with aconventional battery charger 91, also referred to as a "line powercharger", which is optimally mounted on board the vehicle, after thecharge level of run battery 20 drops to the predetermined charge levelwhere a recharge is required. The normal battery recharge procedure froma conventional external 115 or 220 volt power outlet 90 would be toconnect a power cord 93 between outlet 90 and a vehicle connector 92 andprovide battery charge current with on board battery charger 91.

Run battery 20 may be recharged using alternator 40 when an externalsource is not available. However, this essentially eliminates the fueland cost savings obtained by using run battery 20 to power the vehicleloads R_(L) and R_(A). The output line L7 of BSOC channel 60b may beused to provide a recharge warning signal for a display located on theinstrument panel, e.g., illuminating a lamp, tone generator, or otherindicator (not shown). This warning signal advises the vehicle operatorthat run battery 20 requires a recharge and that an external wayside orgarage power outlet 90 should be located to recharge run battery 20 assoon as possible. Alternately, the recharge warning would be activatedbased on a charge level that is above the predetermined charge level orwhich causes output line L7 to switch to a low state, thus giving theoperator time to locate a power supply before alternator 40 isautomatically switched in to recharge run battery 20. Further, a chargelevel gauge, similar to a fuel gauge, could be used to display the stateof charge of one or more batteries.

Non-Microprocessor Three Battery Version

Advantageously, a considerable emissions reduction can be realized byheating a small insulated electrically heated converter (EHC) thatoperates in series with the conventional catalytic converter (not shown)or a standard catalytic converter, collectively illustrated as EHCheater coil 320 in FIG. 1. The problem with heating the EHC coil 320during start with conventional battery charging systems that have only astart battery is that approximately 600 amperes of current is drawn fromthe battery during and after start for approximately 20 seconds. Thiscurrent load would prevent start motor 50 from turning over.

It has been realized by the inventor that by using a dedicated heaterstorage battery, e.g., EHC battery 300, a 600 ampere current draw fortwenty seconds reduces the amp-hour charge level in such a battery byonly four amp-hours. It also has been realized by the inventor that a 24volt 120 amp-hour very high discharge EHC battery 300 can produce such afour amp-hour charge, which charge can be replaced by a normalalternator 40 or by an externally powered battery charger 91, in arelatively short period of time, e.g., between ten to forty minutes,more typically about fifteen minutes.

Both the non microprocessor and microprocessor based systems describedherein can be configured to either recharge EHC heater battery 300 aftereach 20 second heating period during vehicle start, or allow EHC battery300 to be deeply discharged (i.e., down to a preselected charge level)before recharging it, preferably from an external power line source 90,or from alternator 40.

The EHC heater system of the present invention also could be used toinhibit vehicle start for 15 seconds, as is done with diesel enginevehicles to preheat the glow plugs, to apply a preheat to the EHC coil320 for this period and for a 3 to 5 second period after start. TheTable I below indicates the relatively reduced emission levels obtainedduring vehicle start with normal operation and with the preheatoperation of the EHC 320.

                  TABLE I                                                         ______________________________________                                        Preheat Time                                                                           Post Heat  Hydrocarbons                                                                              Carbon Monoxide                               seconds  Time       grams/mile  grams/mile                                    ______________________________________                                         0       18         0.025       0.5                                           15        3         0.017       0.42                                          ______________________________________                                    

In comparison, the emission levels during start when the same vehicleengine is at ambient temperature are: 1 gram of hydrocarbons per mile,and 29 grams of carbon monoxide per mile. Thus, during the period untilthe vehicle engine temperature reaches the steady state temperaturelevel where the conventional catalytic converter properly functions, theEHC battery 300 and coil 320 provide for substantially reducedemissions.

EHC Battery Control System

When wiper W1 of ignition switch 30 is turned to the start position atcontact 32, a high state voltage turn-on signal is sent to a timercircuit 352. The turn-on signal initiates a twenty second output pulseon output L52 of timer 352. The twenty second pulse has a high statewhich turns on a solid state switch 332EHC for the duration of thetwenty second period.

At this time, the engine temperature is monitored by a thermistorcircuit 350. Circuit 350 provides a low state output voltage when theengine temperature is below a predetermined level which is not highenough to heat sufficiently the catalytic converter and a high stateoutput voltage when the engine temperature is above the predeterminedlevel, e.g., 500° F. In the instance where the engine temperature islow, engine thermistor circuit 350 sends a low state signal on outputline L18 to solid state switch 331EHC, which turns switch 331EHC on.Assuming that the twenty second period has not ended, this completes thepath for current flow from EHC battery 300 which energizes EHC solenoidcoil 323. The solenoid coil 323 pulls in contacts 322 and 324 which areganged together. EHC battery 300 is preferably a 24 volt battery andclosing contact 322 delivers 600 amperes of current (I_(EHC)) to EHCheater coil 320. Closing contact 324 shorts the shunt 303 in series withbattery 300 to avoid over heating shunt 303 during the period thatbattery 300 is delivering 600 amperes. When shunt 303 is a length ofwire between two contact pins, or when no BSOC channel 60c is used,contact 324 may be omitted.

At the end of the twenty (20) second timing period, the output voltageon output line L52 of timer 352 drops from a high to a low state.Consequently, solid state switch 332EHC is turned off and contacts 322and 324 both open. This removes the EHC heater current I_(EHC) to coil323 and switches out battery 300.

In the event that the engine temperature is above the predeterminedlevel, it is not necessary to apply heater current to EHC heater coil320. In this case, although the output voltage from timer circuit 352 online L52 is in the high state (during the pulse period) and switch332EHC is on, solid state switch 331EHC is turned off. This inhibitscurrent flow to solenoid 323 and leaves contact 322 open.

The release of contact 324 also places shunt 303 to EHC battery 300 inthe line. The voltage across shunt 303 can therefore be monitored duringrecharge of battery 300 by BSOC channel 60c to determine when battery300 is fully charged (e.g., when a 4 amp-hour charge per EHC 320 heatingevent has been restored), and apply a high state input to NAND gate G1in voltage regulator 42. Because the load current drawn from EHC battery300 by coil 320 and the time period are known, the amp-hour charge lostcan be simulated by a suitable "start" circuit in BSOC channel 60c,which removes an amount of charge from the BSOC integrator capacitivestorage element corresponding to the heater current delivered.Alternately, BSOC channel 60c may simply measure when either a 4amp-hour recharge has been delivered or the charging current to battery300 has dropped to a trickle charge, after each start operation.

The high state voltage output line L306 from BSOC channel 60c also istransmitted to solid state switch 334EHC which turns it on and allowsthe recharge from alternator 40 to be stepped up by circuit 340 from 12volts dc to 24 or 25 volts dc, in order to recharge EHC battery 300.

Module Circuit Descriptions

FIG. 2 illustrates a schematic of the battery state of charge circuitchannels 60a, 60b and 60c, which are preferably identical. The circuitsshown on the schematic of FIG. 2, except current monitoring amplifiersA1 through A4, may be constructed as described in the aforementionedU.S. Pat. Nos. 4,968,940, and 5,179,340 and application Ser. No.07/919,011.

The integrator amplifier 361 in each BSOC channel is an analog type thatintegrates the battery charge current I_(CH) and discharge currentI_(DC) through its shunt (i.e., shunts 11, 21 and 303 and shown in FIG.1), over time. The voltage drop V_(s) across the shunt is proportionalto the current flowing through it. An arbitrary shunt may be selected,e.g., to produce 2.3 millivolts per amp of current, more preferably, alength of battery return cable between two contact pins. A batterycharging current I_(CH) through the shunt produces a positive outputvoltage V_(S) and a discharge current I_(DC) produces a negative V_(S)as illustrated in FIG. 2.

A positive voltage V_(S) causes the integrator output V_(A) to rise asthe battery charges. A negative V_(S) causes V_(A) to drop in thenegative direction over time as the battery discharges. The batterystate of charge can therefore be displayed on a meter in the same manneras a fuel gauge displays the amount of fuel in the tank. Any type ofintegrator, including digital types, will operate equally well in thecircuit.

The integration slope of each integrator circuit 361 has beenarbitrarily established to provide a 2 volt dc output signal to thevehicle display on the output line (lines L361, L362 and L363) when itsbattery (batteries 10, 20 or 300, respectively, in FIG. 1) is fullycharged and an arbitrary low voltage output when the associated batterycharge drops to a level where a recharge is required.

The integrator output voltage V_(A) ramps up and down very slowly overtime and therefore cannot be easily used to operate circuit devices thatperform command functions etc. Consequently, it is necessary to employswitching circuits that either rise from a low to a high voltage or dropfrom a high to low voltage when the output voltage V_(A) is atpredetermined points on the rising or falling voltage ramp as thebattery is being charged or discharged.

Amplifier A4 switches from zero volts to 10 volts dc when the battery isfully charged and the integrator output voltage V_(A) is 2 volts dc.This signals voltage regulator 42 (FIGS. 1, 6) that the battery beingmonitored is fully charged.

Amplifier A3 switches from 10 volts dc to 0 volts when the state of thebattery being monitored drops to an arbitrary, e.g., 50% for a runbattery 20, discharge level. This occurs when the integrator outputvoltage V_(A) drops to 1 volt dc. This signals voltage regulator 42 thata battery is discharged to the point where alternator 40 must be used torecharge it.

Amplifiers A1 and A2 provide a dc output voltage proportional to thecharge and discharge currents through the shunt. These currents varyquite rapidly and consequently produce a rapidly changing positive andnegative going output voltage at the output of A2. The integratorsmooths these rapid changes over time and thus provides a slowly movingoutput voltage V_(A).

The current amplifiers are used to provide display information thatindicates the direction and magnitude of current flow into and out ofthe batteries. The output of amplifier A4 could be used to provide anindication of battery charge level if desired. The charge current I_(CH)into a battery from alternator 40 is very high, approximately 30 amps atthe start of recharge, and drops to a level of approximately 2 to 3amperes when the battery is fully charged. The shunt voltages V_(S)corresponding to these currents could therefore be monitored byamplifier A1 and the output voltage of amplifier A4 used to indicatefull battery charge to voltage regulator 42 in FIG. 1 if desired.

Bad battery cell circuit 364 switches from a zero output voltage to 10volts dc in the event that the battery being monitored has a bad cell.The operation of this circuit is explained in the referenced patentapplications.

The automatic turn on--turn off circuit 362 senses when a small chargeor discharge current produces a small positive or negative voltage V_(S)across the battery current shunt and applies battery voltage (e.g., 12volts) to all the battery state of charge channel circuits. In the turnoff state (standby state) each BSOC channel 60 draws approximately 1milliampere from the battery, e.g., run battery 20. This allows the BSOCchannel 60 to be permanently wired to the battery terminals. When theBSOC channel senses current through the battery, the turn on circuit 362energizes an internal BSOC power supply that provides approximately 50milliamperes of current from the battery to the remainder of the BSOCchannel circuits.

Battery capacity versus temperature circuit 365 provides a signalcorresponding to the change in battery capacity with sensed ambienttemperature. This is a conventional circuit that is commonly used inexisting voltage regulator systems.

Start circuit 363 ensures, during vehicle start, that the integratoramplifier 361 of BSOC channel 60a measures the proper amount of chargeremoved from start battery 10 by starter motor 50. In the case thatshunt 303 is a resistor in series with EHC battery 300, a similar startcircuit 363 may be used to simulate the discharge of current acrossshorted shunt 303 for EHC battery 300 so that integrator amplifiercircuit 361 of BSOC channel 60c measures the proper amount of chargeremoved from battery 300 by EHC coil 320.

Referring to FIG. 3A, solid state start battery switch 32SB, includestwo pnp transistors 3AQ1 and 3AQ3 which are in the on state when bothnpn transistors 3AQ2 and A3Q4 are conducting. This occurs when the inputon line L3 (i.e., the input from wiper W1 of ignition switch 30) is highand the input on line L25 (i.e., the output from BSOC channel 60a) islow. Switch 32SB is off for all other input conditions.

Referring to FIG. 3B, solid switches 332EHC and 34AC each include a pnptransistor 3BQ1, which is in the conducting state when npn transistor3BQ2 is conducting. This occurs when the respective input, line L52 fromtimer circuit 352 or line L34 from NAND gate G2, is high.

Referring to FIG. 3C, solid state switch 331EHC includes transistor 3CQ1which is in the on state when transistor 3CQ2 is conducting. This occurswhen the input on line L18 from engine thermistor circuit 350 is low.

Engine thermistor switching circuit 350 is shown in FIG. 4. Circuit 350senses the temperature of the engine housing near the electricallyheated catalytic converter. The thermistor TR2 is a negative coefficienttype device having a series resistance that reduces as enginetemperature rises. When the engine temperature has reached apredetermined level, the resistance of thermistor TR2 drops to the pointwhere the voltage on line L51 drops below the reference voltage on lineL49. This causes the output line L18 of operational amplifier 4A1 toswitch from a low to a high voltage state. The reference voltage may beprovided in any manner, e.g., a voltage divider between a +12 voltsource across a 10 kΩ resistor and a 4 v zener diode as illustrated inFIG. 4.

Pendulum circuit 70, shown in FIGS. 1 and 5, includes a potentiometer 71having its wiper W-71 operated by a pendulum 72. When the vehicledecelerates, pendulum 72 swings in the "vehicle forward" direction andmoves wiper W-71 of potentiometer 71 in a direction that produces asudden change, e.g., an increase in both the rate of change andmagnitude of the voltage output on line L45. The sudden change inmagnitude and rise time of the voltage on line L45 is sensed bydeceleration circuit 90 and the output voltage on output line L46switches from a low state to a high state output voltage.

Proper selection of the resistive and capacitor components indeceleration circuit 90 will cause the output of switching amplifier 5A3to switch when vehicle deceleration exceeds any predetermined rate. Inthis regard, capacitor C1, resistors R1 and R2 and amplifier 5A1comprise a conventional differentiator circuit that will not produce anoutput voltage unless the vehicle decelerates at a rate greater than apredetermined level. The magnitude of the voltage at the output ofamplifier 5A1 is given by:

    Eout=R1×C1×(E2-E1)/(t2-t1)

Proper selection of component values in the differentiating equationwill produce an output voltage having the proper magnitude for apredetermined vehicle deceleration rate.

The voltage at the output of amplifier 5A1 is amplified by amplifier 5A2and applied to the non-inverting input of amplifier 5A3. When theapplied voltage exceeds the reference voltage provided on the invertinginput of amplifier 5A3, amplifier 5A3 switches from a low state to ahigh state.

Alternately, pendulum circuit 70 can be replaced with any type ofvehicle deceleration detection circuit device, including wheel speedpickoff types, that can be modified to provide an output voltage havinga magnitude and rise time sufficiently proportional to vehicledeceleration to operate with deceleration circuit 90.

Referring now to FIG. 6, voltage regulator 42, in accordance with thenon-microprocessor controlled version of the present invention, issimilar to many off-the-shelf type of voltage regulators that controlthe magnitude of the output voltage V_(A) of alternator 40. Theregulation principle is well known and has been in use almost as long asthe automobile has been in existence. Early voltage regulator circuitssensed the level of the output voltage V_(A) from the alternator 40 andcommanded a relay contact to remain closed for a longer period of timethan open when the output voltage V_(A) was below a preset level, suchas 14.0 volts dc. When the sensed output voltage V_(A) was above thereference level, the contact was commanded to remain open for a longerperiod of time than closed. This switching action maintained the outputvoltage V_(A) in the vicinity of 13.6 volts dc in a reasonable manner.

The voltage regulator circuit also sensed the ambient temperature andmodified the on-off switching time as a function of temperature. It alsomodified the switching on-off time to cause the contact to remain on fora slightly longer period when ambient temperature was low and to remainoff for a slightly longer period of time when the ambient temperaturewas high. This raised alternator nominal 14.0 volt dc output level to14.8 volts at low temperatures and reduced the nominal 14.0 volt outputto 13.6 volts dc at high ambient temperatures. The nominal outputvoltage, when raised to 14.8 volts dc, provided more current to thealternator rotor coil 44R at low ambient temperatures and less currentwhen it was reduced to 13.6 volts at high ambient temperatures, thusmaintaining a proper charging current to the start battery under alldriving and ambient temperature conditions.

Relay contact controlled voltage regulators have been replaced with morereliable transistor switching types that control the alternator rotor,and thus field current, in much the same manner as described above,i.e., by changing the duty cycle of the current.

In accordance with the present invention, referring to FIG. 6, voltageregulator 42 includes an on-off switching circuit comprised of a logicNAND gate G1, a pnp transistor Q606, temperature sensitive diodes 6D1,6D2, zener diode 6Z1, operational amplifier 6A1, voltage dividerresistors 6R1, 6R2 and darlington power switching transistors 6Q1 and6Q2.

When wiper W3 of ignition switch 30 is placed in the run position(contact 37) prior to start, an exciter current from start battery 10 isdelivered through rotor coil 44R of alternator 40 and series transistor6Q2 to ground. This provides sufficient current to overcome the residualmagnetism in rotor coil 44R which allows coil 44R to develop therequired current to operate properly alternator 40.

There are a variety of solid state switching voltage regulators inoperation at the present time. Most of them can be activated anddeactivated to switch the current into rotor 44R on and off by groundinga key signal line in the circuit. This can be manually done with aswitch and automatically done with inputs of the type illustrated inFIGS. 1 and 6 or with a microprocessor.

When the output voltage V_(A) of alternator 40 is below a nominal 14.0volt dc level, zener diode 6Z1 does not conduct current. Consequently,the voltage at its base on top of resistor 6R3 is zero. The sensedalternator output voltage V_(A) is, however, present at thenon-inverting input to amplifier 6A1, thus causing it to switch to ahigh state output voltage level. This causes transistors 6Q1 and 6Q2 toturn on. This in turn causes current to flow through rotor coil 44Rwhich raises the current in field windings 703. The increased current infield windings 703 (stator coils 44S) raises the alternator outputvoltage V_(A) above 14.0 volts. The output voltage V_(A) is produced bythe phase rectifier bridge comprising diodes 7D4, 7D5, 7D6, 7D7, 7D8,and 7D9 (and the feedback output voltage V_(A2) is provided by anexciter bridge comprising diodes 7D1, 7D2, 7D3) in a conventionalmanner.

When output voltage V_(A) rises above 14.0 volts, zener diode 6Z1conducts current and a voltage appears at the inverting input ofamplifier 6A1 that is higher than the voltage on the non-invertinginput. This causes amplifier 6A1 to switch from a high voltage state toa low voltage state, thus turning transistors 6Q1 and 6Q2 off. Thisreduces the output voltage V_(A) below 14.0 volts.

This on-off switching action maintains the alternator output voltageV_(A) at 14.0 volts dc, regardless of changes in the alternator shaftrotational speed.

The forward voltage drop of diodes 6D1 and 6D2 decreases at hightemperature which increases the voltage level at the top of zener diode6Z1. This causes zener diode 6Z1 to turn off the voltage regulator 42earlier in the switching cycle. This causes the nominal alternatoroutput charging voltage to drop to a selected level below 14.0 volts.

The forward voltage drop of diodes 6D1 and 6D2 increases in a lowambient temperature which decreases the voltage level at the top ofzener diode 6Z1. This causes zener diode 6Z1 to conduct later in eachswitching cycle. This causes the nominal alternator output chargingvoltage to increase above the 14.0 level.

Diode 6D1 could be placed near start battery 10 to obtain a bettermeasure of battery temperature. Alternately, a more suitable temperaturesensitive circuit could be used in its place.

The voltage regulator circuit 42 described above is disabled by reducingthe base voltage of transistor Q606 to zero. This occurs when all theinputs to NAND gate G1 are in a high state and the input on line L46 isa low state. This set of conditions causes the output of NAND gate G1 toswitch to the low state and turn transistor Q606 on. When transistorQ606 switches on it reduces the voltage level on line L606 to thenon-inverting input of amplifier 6A1 to zero. This prevents amplifier6A1 from turning voltage regulator 42 on.

When the overriding deceleration input from circuit 90 on line L46 goesto the high state during vehicle deceleration, the base of transistorQ606 is raised, regardless of the input signal levels to NAND gate G1.This causes transistor Q606 to turn off, thus allowing amplifier 6A1 tooperate voltage regulator 42 as required. When any of the lines L6, L7and L306 are in the low state, the output of NAND gate G1 switches tothe high state, thus raising the base of transistor Q606, and enablingvoltage regulator 42. When all three lines L6, L7 and L306 are in thehigh state, regulator 42 is disabled (unless overridden by a high stateinput on line L46 from the deceleration circuit 90).

Logic NAND gate G1 can be replaced, if desired, by a manual switchoperated by the driver. A manual switch can be used to turn voltageregulator circuit 42 on and off in order to switch alternator 40 in andout of the system. A second manual switch could be used to turn solidstate switch 32SB on and off to switch start battery 10 in and out ofthe system.

A meter indicating the state of charge of each battery could be locatedalong with manual solid state switch controls on the instrument panel ofthe vehicle or in another suitable location. It is to be understood thatall of the functions described above and illustrated in FIGS. 1-6 couldbe performed by manually operated switches if desired.

MICROPROCESSOR SYSTEM CONTROLLED EMBODIMENT OF THE INVENTION

Vehicle Run and Battery Charge Control With a Microprocessor

The non-microprocessor embodiment of the invention described above doesnot require the sophistication of a microprocessor to control the levelof alternator current required to provide rectified output current tothe batteries and vehicle loads or alternately to allow the run batteryto provide all the vehicle load current.

Nevertheless, there are advantages afforded by using a microprocessorcontrolled voltage regulator including the ability to operate a complexvoltage regulator, to operate a complex display, complex decision makingcapability, reprogramming flexibility, and a less complex vehicleinstallation (both as original vehicle equipment and as an aftermarketretrofit apparatus) than the non-microprocessor version.

Most four to sixteen bit microprocessors having suitable memory capacitycan be used to replace the discrete circuit non-microprocessor basedvoltage regulator described in the non-miroprocessor system version ofthe invention, as will be clear from the following.

Referring to FIG. 7, one suitable microprocessor 200 is a 16-bitmicroprocessor, Model No. 8397-90, which is available from Intel. Thismodel microprocessor includes a 10-bit analog-to-digital converter,interrupt source inputs, a pulse width modulated output port, a 232 byteregister, memory to memory architecture, a 16×16 bit multiplier, a 32 by16 bit divider, a full duplex serial port, five 8 bit input/outputports, watchdog timers, four 16 bit timers, two external 64K (8K by 8bits) memory devices, a one milliamp standby current drain, and adisplay driver interface including an eight segment liquid crystaldisplay 80 and a 6×6 button keyboard 82.

One suitable memory device 845 for use with microprocessor 200 is EPROMModel P27C64/87C64, which is available from Intel. This device includestwo 64K (8K×8 bit) memory units which are conventionally connected tothe Intel model 8397-90 microprocessor. The pin designations are thoseprovided by the manufacturer. Instructions for programming the IntelModel 8397-90 microprocessor can be found on pages 19-10 through 19-27of the Intel Automotive Handbook, part order number 231792-002,available from Intel.

In the preferred embodiment, microprocessor 200 is provided withsuitable software program instructions in memory so that the vehicleoperator can obtain and display information regarding time, date, analarm function, estimated time of arrival, time on remaining fuel torecharge station, time on remaining fuel to an empty fuel tank, theremaining distance to go on a trip, the distance to travel since thefuel tank was last filled, and the distance to travel on the remainingfuel. Many of these functions may be programmed in a conventional mannerby a person of ordinary skill in the art. Devices commonly referred toas trip computers, which incorporate many of these functions, have beencommercially available in automotive vehicles at least since 1986.

In accordance with the present invention, microprocessor 200 also may beprogrammed to provide information regarding fuel efficiency and fuelbeing consumed in the fuel tank (based on the octane reading of thefuel). This would include average fuel efficiency and miles per gallon,the instantaneous fuel efficiency, the total fuel used on the trip sincethe trip began, the fuel used since the tank was last refilled, and thefuel left in the tank. Also, the microprocessor 200 may provideinformation regarding how long the vehicle may continue operating untilan external battery recharge is required, the time required to rechargerun battery 20 after alternator 40 is switched back in to recharge runbattery 20, and how long the vehicle may safely operate in the run statebefore requiring a recharge. It is noted that in the run state refers toalternator 40 being either switched out or operating at a reducedvoltage output that merely maintains a trickle charge on run battery 20without attempting to fully recharge battery 20.

Also, microprocessor 200 may provide information regarding averagevehicle speed and may include an anti-theft capability, based onrequiring the driver to enter a code on the keyboard 82 prior tostarting the vehicle. Microprocessor 200 also may be utilized to monitorvehicle inputs not indicated above for vehicle diagnostic purposes. Bysampling the alternator output load conditions, battery current levels,battery state of charge levels (in amp-hours), and alternator voltagelevels, in addition to other vehicle sensory inputs, microprocessor 200can perform many useful diagnostic functions. For example, a gradualinability to recharge properly any of the batteries, or for any batteryto provide appropriate load currents upon demand in certain situations,can result in a diagnostic message indicating a problem with either thegiven battery, alternator 40, the wiring harness of the vehicle, vehicleloads (R_(L) and R_(A)), or even battery terminal connections.Microprocessor 200 also can be programmed to identify the followingdiagnostic conditions: a bad battery, a malfunctioning alternator, ashort in a vehicle accessory or wiring harness causing excessive currentdrain, a bad diode bridge, the onset of a load dump condition, and otherrelated diagnostic matters based on sensed states-of-charge, voltagesand currents over time. The bases for these determinations are morefully described in the copending and commonly assigned application Ser.No. 07/919,011.

The input/output circuits 744, 745, 746, and 747 which interfacemicroprocessor 200 and the vehicle sensor signals, are standard scaling,gain, and reset circuits. The design and construction of these circuitsas well as the programming of microprocessor 200 are within theabilities of the person of ordinary skill in the art, are well known,and do not require elaboration.

In this embodiment, a pulse width modulated signal is output on line L39at pin 39 of microprocessor 200, when it passes through input outputinterface circuit 747. The corresponding pulse width modulated outputfrom circuit 747 on line L747, which is input to the darlington drivetransistors 7Q1 and 7Q2, is a pulse train having a fixed period of 256state times and a programmable width of from 0 to 255 state times. Pulsewidth is programmed by loading the desired value for optimum fueleconomy, as determined by microprocessor 200, into a microprocessorpulse width modulation (PWM) control register (not shown). The variednumber of state pulses over the 256 pulse period determines the averagecurrent provided by drive transistors 7Q1 and 7Q2 in FIG. 7 to the coilof rotor 44R of alternator 40. Rotor 44R generates a conventional threephase electromagnetic field voltage in the stator coils 44S (see alsocoils 703 in FIG. 6) having a magnitude proportional to the level of thedc input field current I_(F). The alternating field current of thestator coils 44S is then rectified by diode bridges 740 (diodes 7D1,7D2, 7D3) and 742 (diodes 7D4, 7D5, 7D6, 7D7, 7D8, 7D9) to provide thedc output voltage V_(A) on line L5.

Preferably, microprocessor 200 is programmed for receiving andprocessing the various sensor input parameters and controlling thealternator 40 output voltage V_(A) on line L5 between alternator 40 andrun battery 20 over the range of 0 to 17 volts, according to a set ofdefined operating conditions stored in a look-up table or an algorithm.Preferably, look-up tables are used which comprise data curves of, forexample, alternator output voltages (start and run conditions, includingEHC preheat operations) versus various vehicle load and ambienttemperature conditions, states of charge, and other data useful for theaforementioned diagnostic purposes. The data curves preferably correlatethe range of sensor parameters and predetermined operating conditionsand, in response to the determined inputs, provide a suitable outputvoltage to maximize fuel economy. The look-up tables utilized by themicroprocessor may be empirically derived according to the specificvehicle operating conditions, operating mode, and batterycharacteristics.

In this embodiment, microprocessor 200 may monitor ambient temperatureconditions and engine speed and regulate the bias of the alternatoroutput voltage in a conventional manner. In accordance with the presentinvention, microprocessor 200 also may monitor the charging currentI_(CH) by sensing the voltage signal representing the deceleration ofthe vehicle, and the state of charge and current signalscharge/discharge from BSOC channels 60a, 60b and 60c.

These sensed parameters are then compared to data in the look-up tablesand an appropriate output voltage is selected. The look-up table anddata stored in memory device 845 provide fuel economy calculationinformation. Software for microprocessor 200 and the look up tables andalgorithms may be created in a conventional manner using an emulatorboard and stored in memory 845.

A watchdog circuit (not shown in FIG. 7), is located between pins 55 and45 of Intel model 8377-90 microprocessor 200 and provides a gracefulrecovery from software errors. In this regard, a 16 bit counter inmicroprocessor 200 will count state times until it overflows. If anoverflow occurs prior to correction of an error, microprocessor 200 isreset. A clock 204 is used for state timing and other signal processingfunctions. Preferably a 12 MHz clock 204 is employed.

Referring to FIG. 7, the interconnection between microprocessor 200,keyboard 82 and display 80 is shown. In this embodiment, keyboard 82 isa conventional 6×6 keyboard having vertical and horizontal contact lineslaid out in a 6×6 grid, and an associated eight character LCD display80. Such keyboard devices can be readily implemented using the Intel8397-90 microprocessor. Six of the keyboard lines are connected alongline L32B-A, which is a parallel data bus, to pins P2.6, P2.7, P4.7,P4.0, P0.1, and P0.0 on microprocessor 200. The pin numbers are notshown in FIG. 7 for clarity of illustration. The other six keyboardlines are connected by line L32B-B, also a parallel data bus, to pinsP4.1-P4.6 on microprocessor 200. The key designation of keyboard 82 isselected by appropriate programming of intersecting contact lines.

Outputs P1.0-P1.4 of microprocessor 200 are connected by line L24B-A, aparallel data bus, to a binary coded decimal digit driver circuit 81,which in turn is connected to display 80. Also, microprocessor 200outputs P3.0-P3.7 are connected along line L24B-B, a parallel data bus,to segment driver 83, which, in turn, provides information to display80.

In this driver interactive system, the driver may select which conditionof the vehicle or which diagnostic parameter or trip computer functionto display at any given time. Accordingly, specific keys in keyboard 82may be dedicated for displaying state of charge of run battery 20, startbattery 10 or EHC battery 300 upon actuation. Alternatively, the keyfunctions may be selected according to a displayed menu of selections,such that different keys have different functions depending on the menuselected.

In addition, microprocessor 200 may be programmed to display the stateof charge measures automatically when the state of charge of therespective battery falls below a preselected level or to display anappropriate message when a diagnostic routine indicates that a problemhas been detected. Such an automatic display may be accompanied by awarning indication, e.g., a indicator light on the instrument panel oran audible tone. A distinctive warning could be used to indicate to thedriver that the vehicle has switched from run battery operation only torunning on the alternator, e.g., during a recharge of run battery 20. Asuitable message also may be displayed to indicate how long it will taketo recharge the battery with the alternator before automaticallyswitching back to run battery operation. Other variations may beselected as a matter of design choice, provided that the selectedmicroprocessor 200 and memory 845 have sufficient processing capability.

The previously discussed microprocessor pulse width modulation (PWM)circuit output on pin 39 and line L39 of microprocessor 200 smoothlyvaries the current to driver transistors 7Q1 and 7Q2, which in turnsmoothly varies the current into rotor 44R in response to system sensorinputs and the dc output level (V_(A2)) of alternator 40 on line L602.

Microprocessor 200 compares the level of alternator voltage V_(A2) online L602 (through interface circuit 747) with a reference voltage levelstored in memory. When V_(A2) is higher than the reference voltage,e.g., a nominal 14.6 volts dc, the duty cycle of the PWM output islowered until V_(A2) returns to 14.6 volts dc. When V_(A2) is below 14.6volts dc, microprocessor 200 increases the duty cycle until V_(A2) is at14.6 volts dc. The nominal 14.6 volt level may be altered if requiredwith a software change.

Microprocessor 200 also senses a signal on line L748 from ambienttemperature sensor circuit 748, which is passed through input outputinterface circuit 745 for scaling and shaping, and accordingly adjuststhe duty cycle of its PWM output on line L39 to vary the alternatorcharging voltage (V_(A2)) between 16.4 and 13.6 volts in accordance withconventional battery charging current versus temperature requirements.

When wiper W1 of ignition switch 30 is turned to the start position, asshown in FIG. 1, ignition switch contact 32 provides current to actuatestart solenoid 31 which pulls in contact 52 thus allowing start battery10 to provide the current required to operate start motor 50.Microprocessor 200 also actuates EHC solenoid coil 323 during vehiclestart by turning on solid state switches 331EHC and 332EHC for aselected timing period of twenty seconds. When switches 331EHC and332EHC are turned on, as noted, solenoid 323 pulls in ganged powercontacts 322 and 324. Power contact 322 routes heater current from EHCbattery 300 to the EHC heater coil 320 and contact 324 shorts out shunt303. At the end of the selected timing period, microprocessor 200 openssolid state switches 331EHC and 332EHC. In the event that microprocessor200 detects a signal from engine thermistor circuit 350 that correspondsto the engine temperature being above a preselected "hot" temperature,microprocessor 200 opens solid state switch 331EHC, which preventscurrent from reaching the EHC solenoid coil 323, thus preventing heatercurrent from flowing into the EHC heater coil 320. Separate controllines L331 and L332 respectively connect microprocessor 200 to switches331EHC and 332EHC. It should be understood that, rather than a timingperiod, a first signal could be used to close switches 331EHC and thethermistor circuit 350 could be used to open circuit the switch once theengine has reached the desired temperature.

When wiper W1 is returned to the run position, as indicated in FIG. 7, ahigh input signal is applied on line L35 through I/O circuit 745. Thishigh signal is sensed by microprocessor 200 which, in response, monitorsthe outputs of BSOC channels 60a, 60b and 60c on lines L25, L6 and L306respectively, and maintains the output voltage of alternator 40 at alevel required to recharge the start, run and EHC batteries 10, 20 and300 in accordance with ambient temperature requirements. This chargingcontinues until their respective charge levels are above a predeterminedpoint. Again, as in the non-microprocessor version, contact 324 may beomitted where the shunt 303 is a length of battery cable, and BSOCchannel 60c may be omitted.

When microprocessor 200 receives signals on lines L25, L6 and L306 fromBSOC channels 60a, 60b and 60c respectively indicating that all threebatteries are recharged, it reduces the PWM duty cycle on line L39 tocause the alternator output voltage V_(A) to drop to a level low enoughto allow the terminal voltage of run battery 20 to back bias therectifier diodes 742 on line L5. This removes the engine torque from theshaft of alternator 40 and allows the run battery 20 to provide all thevehicle load current. This is the preferred mode of operation formaximum fuel savings.

Thereafter, when microprocessor 200 receives a signal on line L7 fromBSOC channel 60b that indicates run battery 20 state of charge is belowa predetermined charge level, microprocessor 200 increases thealternator output voltage to a point where it can operate the vehicle insuch a manner that it provides the required load current and a rechargecurrent to run battery 20. (Alternately, the alternator output voltageis raised to a point where run battery 20 does not discharge further,but is not necessarily recharged.) The driver is also warned by display80 that a source of charge external to the vehicle should be located assoon as possible to recharge run battery 20. An on board battery chargeris preferably provided (not shown in FIG. 7, see FIG. 1).

Microprocessor 200 also monitors battery recharge current on lines L390,L391 and L392 which are respectively passed through input output circuit744, to determine when recharge occurs. (See the output of amplifier A2on FIG. 2).

In this embodiment, a wheel speed indicator circuit 95 is provided.Circuit 95 includes a permanent magnet 96 on a wheel speed ortransmission shaft 97. It produces pulses proportional to wheel speedwhich are sensed each time magnet 96 passes a stationary pickup coil 98.Consequently, a train of pulses having a period inversely proportionalto wheel speed is transmitted on line L95 to a pulse squaring circuit99. The output of pulse squaring circuit 99 is transmitted on line L99,passed through input output interference circuit 745, to microprocessor200. Microprocessor 200 thus can sense and record vehicle instantaneousspeed, average speed, deceleration, and acceleration. It can use thisinformation in the software program for controlling the system inresponse to these inputs. Vehicle deceleration, for instance, iscomputed by calculating the reduction in vehicle speed over a given timeperiod. In particular, the use of wheel speed circuit 95 makes thependulum circuit 70 of the non-microprocessor embodiment (see FIG. 1)unnecessary in the microprocessor controlled embodiment.

When microprocessor 200 senses vehicle deceleration it increases theoutput voltage V_(A2) of alternator 40. As a result, the vehiclemomentum, rather than the engine, is used to apply torque to thealternator shaft and provide a recharge current for charging run battery20. This procedure applies recharge current without any fuelexpenditure, and effectively extends the time the vehicle loads R_(L)+R_(A) can be operated off of run battery 20 without requiring anexternal recharge or recharging battery 20 by burning fuel.

Microprocessor 200 provides the operational advantage of not having toreduce the excitation current completely from rotor 44R of alternator 40when the system is operating with run battery 20 providing current tothe vehicle electrical loads. Microprocessor 200 can, in response tosensor inputs, provide a pulse width modulated current having a dutycycle just sufficient to provide the lowest possible current toalternator rotor 44R required to avoid sharing current with run battery20 when it is being used. This removes the alternator torque from theengine as effectively as when all the current is turned off to rotor44R.

The current to rotor 44R can be smoothly varied by microprocessor 200 tovary the output voltage level of alternator 40 to allow it to (a) shareany portion of its output current to the vehicle loads along with runbattery 20, (b) share none of its output current with the run battery20, or (c) provide all of its output current to the vehicle loads andcharge run battery 20. The desired alternator operating mode, a, b or c,above could be programmed from keyboard 82 by the system operator.

Microprocessor 200 also provides the capability of being reprogrammed toaccommodate changing vehicle operating requirements that may occurbetween vehicles and with the addition of options.

Current outputs from BSOC channels 60a, 60b, and 60c on lines L390,L391, and L392, respectively, also are sensed by microprocessor 200 atthe corresponding outputs of I/O circuit 744. The direction andamplitude of the currents into and out of batteries 10, 20 and 300 onthe above lines are monitored for control and display purposes.

Microprocessor 200 also monitors the battery current in each of shunts11, 21, and 303 for diagnostic and reset purposes. Failure of the chargecurrent to drop below a preselected level on lines L390, L391 and L392when the state of charge voltage of the monitored battery is above apreset level on lines L25, L6 and L306 respectively, is an indication ofa bad cell in the associated battery.

Microprocessor 200 may be used to turn off automatically selectedvehicle electrical accessories when the vehicle is parked, the ignitionkey is in the accessory position, and the start battery state of chargeis below a preselected level. In this regard, a high voltage statesignal from the "PRNDL" gear shift circuit 15 is transmitted on line L15(through I/O circuit 745) when the shift lever (not shown) is in thepark "P" position. A high voltage state signal also is transmitted online L38 (passed through I/O circuit 745) when ignition switch wiper W4is in the accessory position (contact 38) and a low voltage level signalis transmitted on line L25 when the state of charge of start battery 10is below a preselected level. When these three conditions are satisfied,microprocessor 200 transmits a turn off signal on line L34 to solidstate switch 34AC which removes battery discharge current from selectedvehicle accessories R_(L) and R_(A).

EXAMPLES

The advantages of the present invention are illustrated with referenceto the fuel consumption test drives made with a 1988 General MotorsOldsmobile Cutlass, shown in FIG. 8, and a 1984 Ford Mercury Lynx, shownin FIG. 9.

All fuel measurements were made based on two-hour runs, under theweather conditions described below and the load currents on thealternator specified. Plot 8A represents highway driving in warm and dryroad conditions. Plot 8B represents a combination of city and highwaydriving in light to heavy traffic and cool and raining road conditions.Plot 8C represents suburban driving in cool and dry road conditions.Plot 8D represents city driving in cool and dry road conditions. Plot 8Erepresents city driving in heavy traffic in cool and dry roadconditions. Plot 9A represents highway driving. Plot 9B representssuburban driving in light traffic. Plot 9C represents suburban drivingin heavy traffic. Plot 9D represents city driving in heavy traffic. Forhighway traffic, each car was driven one hour in one direction and onehour in the opposite direction, to balance out windage and otherfactors. Similarly, for suburban and city traffic, the path followedduring one hour was essentially reversed during the second hour.

The current load on the alternator was varied by turning on variouselectrical devices in the car (such as the radio, windshield wiper,headlights, etc.), and was measured by one shunt in series with thealternator and one shunt in series with the battery. The fuelmeasurements were made by connecting a first fuel-flow meter in serieswith the gasoline tank supply line and a second fuel-flow meter inseries with the fuel pump return line and subtracting the difference.

The percentage fuel savings achieved by operating at zero-loadconditions, as compared with various current load conditions, can becalculated by the expression: ##EQU1## wherein MPG₀ is miles per gallonat zero current load on the alternator and MPG_(LOAD) is miles pergallon at the selected load conditions and current load in amps.

The percentage fuel savings for the 1988 Oldsmobile Cutlass are shownbelow under Table I and in FIG. 8, while those for the 1984 Mercury Lynxare shown under Table II and in FIG. 9. The average of both is shownunder Table III. The current load at 18 amps is a hypothetical drivingcondition based on the curves in FIGS. 8 and 9. With respect to TableIII, the overall average includes highway, suburban and city driving,assuming that there is an equal amount of driving in each of thesecategories.

In FIGS. 8 and 9, the parenthetical numbers correspond to (amps, milesper gallon) (% fuel savings).

                  TABLE I                                                         ______________________________________                                        1988 OLDSMOBILE CUTLASS                                                                                      Current                                                                              %                                                                      Load   Fuel                                    Driving Conditions                                                                         MPG.sub.O                                                                             MPG.sub.LOAD                                                                            (amps) Savings                                 ______________________________________                                        Highway Traffic                                                                            17.7    17.3      8      2.3                                                  17.7    16.8      18     5.4                                     Warm, Dry    17.7    16.25     26     8.9                                     Conditions   17.7    14.64     46     20.9                                    Highway and City                                                                           17.0    16.5       8     3.0                                     Traffic      17.0    16.3      18     4.3                                     Rainy, Cool  17.0    15.9      26     6.9                                     Conditions   17.0    13.8      46     23.2                                    Suburban Traffic                                                                           12.32   11.9       8     3.5                                                  12.32   11.05     18     7.6                                     Cool, Dry Conditions                                                                       12.32   10.97     26     12.3                                                 12.32   10.3      46     19.6                                    City Traffic 12.0    11.5       8     4.3                                                  12.0    11.1      18     8.1                                     Cool, Dry Conditions                                                                       12.0    10.6      26     13.2                                                 12.0    9.9       46     21.2                                    Heavy City Traffic                                                                         9.7     9.25       8     4.8                                                  9.7     8.8       18     10.2                                                 9.7     8.3       26     16.9                                                 9.7     6.8       46     42.6                                    ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        1984 MERCURY LYNX                                                                                            Current                                                                              %                                                                      Load   Fuel                                    Driving Conditions                                                                         MPG.sub.O                                                                             MPG.sub.LOAD                                                                            (amps) Savings                                 ______________________________________                                        Highway Traffic                                                                            32.5    31.8      8      2.2                                                  32.5    30.8      18     5.5                                                  32.5    30.2      26     7.6                                                  32.5    26.5      48     22.6                                    Suburban Light                                                                             25.5    24.2       8     5.4                                     Traffic      25.5    23.0      18     10.9                                                 25.5    21.5      26     18.6                                                 25.5    18.0      48     41.7                                    Suburban Heavy                                                                             23.2    23.1       8     0.4                                     Traffic      23.2    21.3      18     8.9                                                  23.3    20.5      26     13.2                                                 23.22   16.8      48     38.1                                    City Heavy Traffic                                                                         17.4    16.45      8     5.8                                                  17.4    15.0      18     16.0                                                 17.4    14.0      26     24.3                                                 17.4    11.8      48     47.5                                    ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        Fuel Savings Average for Both Cars                                                                       Percentage                                         Current Load Driving Conditions                                                                          Fuel Savings                                       ______________________________________                                         8 amps      Highway average                                                                             2.5                                                             Suburban average                                                                            3.1                                                             City average  5.0                                                             Overall average                                                                             3.53                                               18 amps      Highway average                                                                             5.1                                                             Suburban average                                                                            9.1                                                             City average  11.4                                                            Overall average                                                                             8.53                                               26 amps      Highway average                                                                             7.8                                                             Suburban average                                                                            14.6                                                            City average  18.1                                                            Overall average                                                                             13.5                                               46 amps      Highway average                                                                             22.2                                                            Suburban average                                                                            33.1                                                            City average  37.1                                                            Overall average                                                                             30.8                                               ______________________________________                                    

The cost savings from recharging run battery 20 from a conventional115-volt line source is illustrated from the information set forth inTable IV. This information compares the cost of fuel to supply each of avery heavy current load, a moderately heavy current load, and a lightcurrent load from the alternator, to the cost of recharging the batteryusing an external line power charger. All of the examples are based on a60 amp-hour and 720 volt-amp-hours discharge/charge (a 12-volt battery)while the vehicle was travelling in highway traffic at 60 mph.

The cost of electricity is based on 11.6¢ per Kw-hr, which is acalculated average rate for electricity (summer and winter) forresidential use in New York City ca. 1991-92, independent of taxes andother charges. Commercial rates for electricity tend to be higherdepending upon volume and time of consumption. If the power source isthe battery, corresponding to no load current from the alternator, thecost of electricity to recharge the battery from an external batterycharger and restore 720 volt-amp-hours (0.72 Kw-hr), at 11.6¢ per Kw-hr,would be 8.4¢. This amount is the same for all examples.

The cost of fuel is based on $1.30/gallon. If the power source is thealternator, such that no current is provided by the battery, the fuelcost for running the electrical load off the alternator would be:##EQU2## The time period is selected to obtain the 60 amp-hour dischargefor the given current load at 60 MPH. The result of the calculationsusing the above formula and the data points on Tables I and II are setforth under Table IV below.

                  TABLE IV                                                        ______________________________________                                              Time       Cost of                                                      Cur-  Period for Operating Cost of                                            rent  60 Amp-Hour                                                                              Off The   Recharging                                                                              Cost Ratio                               Load  Discharge  Alternator                                                                              From External                                                                           Fuel/                                    (Amps)                                                                              (hours)    (¢)  Charger (¢)                                                                        Electricity                              ______________________________________                                        1984 Mercury Lynx - Highway driving at 60 mph                                  8    7.5        39        8.4        4.6/1                                   26    2.3        42        8.4         5/1                                    48     1.25      67.6      8.4         8/1                                    1988 Oldsmobile Cutlass - Highway driving at 60 mph                            8    7.5        76.4      8.4        9.1/1                                   26    2.3        91        8.4       10.8/1                                   46    1.3        $1.20     8.4       14.3/1                                   ______________________________________                                    

Generally, the greater the current load of the vehicle, the greater thesavings when the current load is driven by run battery 20 only, providedthat run battery 20 is recharged by an external line power charger.

The improvement in fuel economy realized by the present invention isproportional to the time the alternator is operated at a relativelyreduced output voltage, e.g., at 12 or zero volts versus 13.6 to 14.7volts.

A 10% fuel saving on every gas powered vehicle in the United Stateswould amount to a reduction of 13.5 billion gallons of gasoline per yearin the USA. This corresponds to saving approximately 20 billion dollarsa year at the retail pump. It also translates into substantial reductionin undesirable gaseous and particulate emissions which result from fuelconsumption.

One skilled in the art will appreciate that the present invention can bepracticed by other than the described embodiments which are presentedfor purposes of illustration and not of limitation.

I claim:
 1. A battery charging system for an automotive vehicle havingelectrical accessory circuits and a starter motor for starting a fuelconsuming engine comprising:a start battery for providing a dischargecurrent for operating the starter motor; a run battery for operating theaccessory circuits; a first device for monitoring the state of charge ofthe start battery; a second device for monitoring the state of charge ofthe run battery; an alternator having a variable output conditionincluding a regulated output voltage at a selectable level and an outputcurrent, said alternator being driven by the engine; a first circuit forelectrically connecting the alternator output to the start battery forcharging the start battery; a second circuit for electrically connectingthe alternator output to the run battery for charging the run battery;and a control circuit for selecting and controlling the output conditionof the alternator in response to the sensed states of charge of thestart battery and the run battery, such that a first alternator outputvoltage level is normally selected when the sensed state of charge ofthe start battery is at or above a first preselected charge level andthe sensed state of charge of the run battery is at or above a secondpreselected charge level, and the alternator produces less countertorque on the engine when the first alternator output voltage level isselected relative to the counter torque produced at other times when asecond output voltage level, greater than the first output voltagelevel, is selected.
 2. The system of claim 1 wherein the alternatoroutput hasthe second alternator output voltage level and a chargingcurrent when the sensed state of charge of the start battery is belowthe first preselected charge level, and a third alternator outputvoltage level and a charging current when the sensed state of charge ofthe start battery is at or above the first preselected charge level andthe sensed state of charge of the run battery falls below the secondpreselected charge level.
 3. The system of claim 2 wherein the secondand third voltage levels are the same.
 4. The system of claim 2 whereinthe second voltage level corresponds to rapidly recharging the startbattery.
 5. The system of claim 2 wherein the third voltage levelcorresponds to rapidly recharging the run battery and the controlcircuit further comprises means for maintaining the alternator output atthe third voltage level after the run battery state of charge fallsbelow the second preselected charge level until the run battery is fullycharged.
 6. The system of claim 2 wherein the third voltage levelcorresponds to placing a trickle charging current on the run battery. 7.The system of claim 1 wherein the first preselected charge levelcorresponds to the start battery having a full state of charge and thesecond preselected charge level corresponds to the run battery having astate of charge that is selected from between 40% and 100% of a fullcharge.
 8. The system of claim 1 wherein the first voltage levelcorresponds to no charge current being provided by the alternator to therun battery and the start battery.
 9. The system of claim 1 furthercomprising a display means for indicating the run battery state ofcharge.
 10. The system of claim 1 further comprising a display and meansfor selecting to display one or more of the start battery state ofcharge, run battery state of charge, the time required to recharge therun battery, wherein the display is responsive to the selecting meansfor displaying the selected information.
 11. The system of claim 1wherein the first circuit further comprises a switch for disconnectingthe start battery from the alternator output.
 12. The system of claim 11further comprising a circuit for automatically operating the switch fordisconnecting the start battery from the alternator output when thestart battery state of charge indicates that the start battery is fullycharged.
 13. The system of claim 1 wherein the second circuit furthercomprises a switch for disconnecting the run battery from the alternatoroutput.
 14. The system of claim 1 further comprising a switch forconnecting the run battery and the start battery in parallel.
 15. Thesystem of claim 1 wherein the alternator and the control circuit furthercomprise:an alternator having a rotor coil and stator coils forproviding an alternating current in response to a control current on therotor coil; a pulse width modulation circuit for providing a controlcurrent with a selected duty cycle to the rotor coil; a diode bridgehaving a forward-biased condition for producing the alternator outputvoltage and current from the alternating circuit and a reversed-biasedcondition for providing no output current; and means for selecting theduty cycle of the control current, in response to the sensed states ofcharge of the run battery and the start battery, from one of a firstduty cycle corresponding to the first voltage level, a second duty cyclecorresponding to the second voltage level, and a third duty cyclecorresponding to the third voltage level.
 16. The system of claim 15wherein the first duty cycle corresponds to no alternator outputcurrent.
 17. The system of claim 15 further comprising:a device formonitoring when the vehicle is decelerating; and a deceleration circuithaving a first output in response to the vehicle decelerating at a rategreater than a selected threshold rate; wherein the means for selectingthe duty cycle is responsive to the first output of the decelerationcircuit for selecting the duty cycle to be one of the second and thirdduty cycles.
 18. A method for operating a battery charging system for anautomotive vehicle having electrical accessory circuits and a startermotor for starting a fuel consuming engine comprising:providing a startbattery having a discharge current for operating the starter motor;providing a run battery for operating accessory circuits; monitoring thestate of charge of the start battery; monitoring the state of charge ofthe run battery; providing an alternator having a variable outputcondition including a regulated output voltage at a selectable level andan output current, said alternator being driven by the engine;controlling the output of the alternator in response to the sensedstates of charge of the start battery and the run battery, and normallyproducing a first alternator output voltage level when the sensed stateof charge of the start battery is at or above a first preselected chargelevel and the sensed state of charge of the run battery is at or above asecond preselected charge level, such that the alternator generates lesscounter torque on the engine when the first alternator output voltagelevel is produced relative to the counter torque generated at othertimes when a second output voltage level, greater than the first outputvoltage level, is produced; connecting the alternator output to thestart battery for charging the start battery; and connecting thealternator output to the run battery for charging the run battery. 19.The method of claim 18 wherein the alternator output hasthe secondalternator output voltage level and a charging current when the sensedstate of charge of the start battery is below the first preselectedcharge level, and a third alternator output voltage level and a chargingcurrent when the sensed state of charge of the start battery is at orabove the first preselected charge level and the sensed state of chargeof the run battery falls below the second preselected charge level. 20.The method of claim 19 wherein the second and third voltage levels arethe same.
 21. The method of claim 19 wherein the second voltage levelcorresponds to rapidly recharging the start battery.
 22. The method ofclaim 19 wherein the third voltage level corresponds to rapidlyrecharging the run battery and the method further comprises, after therun battery state of charge falls below the second charge level,maintaining the alternator output at the third voltage level until therun battery is fully charged.
 23. The method of claim 19 wherein thethird voltage level corresponds to placing a trickle charging current onthe run battery.
 24. The method of claim 19 further comprisingdisplaying the run battery state of charge.
 25. The method of claim 19further comprising selectively displaying one or more of the startbattery state of charge, run battery state of charge, and the timerequired to recharge the run battery.
 26. The method of claim 18 whereinthe first preselected charge level corresponds to the start batteryhaving a full state of charge and the second preselected charge levelcorresponds the run battery having a state of charge that is selectedfrom between 40% and 100% of a full charge.
 27. The method of claim 18wherein the first voltage level corresponds to no charge current beingprovided by the alternator to the run battery and the start battery. 28.The method of claim 18 further comprising providing a switch fordisconnecting the start battery from the alternator output voltage. 29.The method of claim 28 further comprising automatically disconnectingthe start battery from the alternator output voltage when the startbattery state of charge indicates that the start battery is fullycharged.
 30. The method of claim 18 further comprising providing aswitch for disconnecting the run battery from the alternator outputvoltage.
 31. The method of claim 18 further comprising providing aswitch for connecting the run battery and the start battery in parallel.32. The method of claim 18 in which the alternator includes analternator having rotor and stator coils and a diode bridge having aforward-biased condition for providing a dc output voltage and currentand a reversed-biased condition for not providing an output current inresponse to a control current on the rotor coil, furthercomprising:providing the rotor coil with a control current having aselected duty cycle; and selecting the duty cycle of the controlcurrent, in response to the sensed states of charge of the run batteryand the start battery, from one of a first duty cycle corresponding tothe first voltage level, a second duty cycle corresponding to the secondvoltage level, and a third duty cycle corresponding to the third voltagelevel.
 33. The method of claim 32 wherein the first duty cyclecorresponds to no alternator output current.
 34. The method of claim 32further comprising:monitoring when the vehicle is decelerating; andselecting the duty cycle to be one of the second and third duty cyclesin response to the vehicle decelerating at a rate greater than aselected threshold rate.